Patent GB-186088-A (GB)
Title: Improvements in apparatus for regulating the speed and phase compensation of asynchronous electric machines by means of a commutator machine connected in cascade therewith
IPC: H02K17/38
Filed: 1921-04-11
Abstract: 186,088. Marks, E. C. R., (Siemens-Schuckertwerke Ges.). April 11, 1921. Alternating - current induction machines.-In an arrangement for the speed regulation of an asynchronous machine by means of a commutator machine which is cascaded with the rotor, which can absorb or generate mechanical power, and which is excited by current of the frequency of the supply circuit of the main machine or approximately this frequency, the commutator machine is excited by a synchronous machine. Means may also be provided for enabling the commutator machine to control the phase compensation of the main machine. As shown in Fig. 1, the main asynchronous machine b, which runs on the supply a, is connected by slip-rings c to the stator of the commutator regulating machine e driven by a synchronous machine i from the mains a. The commutator machine is excited by a synchronous machine h feeding slip-rings g. The speed regulation of the main machine is effected by varying the continuous-current excitation of the machine h or by phase transformers. Or, if regulation in steps is required, step transformers may be connected between the exciting-machine and the slip-rings of the commutator machine. Below synchronism, the commutator machine takes electrical power from the rings e converts it into mechanical power and returns it to the supply a electrically through the machine i. By weakening the excitation of the machine h and, therefore, the volts generated at the commutator f, the machine b may be brought up to synchronism, and by reversing the excitation of the commutator machine, the machine b may be brought above synchronism, in which case the machine i supplies the machine h with mechanical power. The commutator machine may be directly driven by the main machine, as in Fig. 8, in which case the exciter h is driven by a synchronous machine m on the supply a so as to feed the rings a with current of the supply frequency. By providing the stator of the commutating machine with a compensating winding, the arrangement eliminates the effect of higher harmonics in the circuits of the main machine, such as occur with singlephase induction machines. Fig. 3 shows the use of such a compensating winding e in an arrangement as in Fig. 1 together with an adjustable shunting resistance r to enable the commutator machine d to be run up as an induction motor. This is done by opening the switches n, l and starting the main machine by means of rotor resistances m so that the machine h feeds the rings g with starting current. When normal speed is reached, the switches are closed. The machine d may alternatively be started as an induction motor while the main machine is stationary and acts only as a transformer on the supply a. The synchronous exciter may also effect phase compensation by having its stator angularly moved or by having an additional exciting winding, as shown in Fig. 4. In this figure, b<1>, b<2> are the stator and rotor windings of the main machine e, f, and g the stator coils, commutator and rings of che commutator machine and h the synchronous exciter which is driven by a synchronous machine i on the supply a and has two independent continuous-current excitation windings k, l displaced by 90‹. These are separately controlled, one for phase compensation and the other for speed regulation of the main machine. Alternatively, the synchronous exciter may be a machine of normal 3-phase wound-rotor asynchronous type but with two of the rotor coils coupled to a star point and supplied with continuous current for, say, speed control and the remaining coil brought out separately to the continuous current supply for the phase-compensating component. The above methods of speed control may be used for fine graduations of speed in combination with a tapped transformer for coarse steps, as shown in Fig. 8. The main and cascaded commutator machines b, d are on the same shaft, and the synchronous exciter h is driven from the supply a by a synchronous motor m as described above. A transformer k has its primary connected to the supply and its tapped secondary l is inserted between the exciter h and the rings g of the commutator machine. In the case of a high voltage supply, the driving motnr m may be connected to tappings on the winding l in place of being fed through a separate transformer on the mains. Specification 186,087 is referred to.